Photochemical reactions for commercial synthesis

ABSTRACT

Photochemical reactions are conducted using polymer beads arranged as a monolayer, e.g. floating on the surface of a moving body of water. The polymer bead is impregnated with a reactant, floated on the water or otherwise exposed as a monolayer in direct sunlight so as to expose the reactant to solar radiation, collected at a downstream location, treated to remove product from the polymer, and then the bead can be recycled. The process can be used to collect and store solar energy in chemical form, or for conducting photochemical synthesis to produce useful chemical products.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.442,181 filed Nov. 16, 1982, and now U.S. Pat. No. 4,525,255.

FIELD OF THE INVENTION

This invention relates to photochemical reactions and more particularlyto a process for conducting photochemical processes, using visible orultraviolet radiation e.g. solar radiation, to produce useful chemicalproducts.

BACKGROUND OF THE INVENTION

The utilization of solar radiation for producing useful chemicalproducts and the production of useful energy has heretofore beenhindered by economic considerations. The surface area of land which mustbe utilized to obtain useful amounts of solar energy, even in solarenergy rich environments such as U.S. desert areas, is enormous usingcurrently available solar energy collectors. All such solar collectionsneed to be mounted and supported on land, in suitable disposition forsolar energy collection. Even the mounting and supporting structuresrequired to cover a sufficient land area to support enough conventionalsolar collectors to supply large amounts of power therefrom areprohibitively expensive.

A further difficulty with solar energy utilization arises from the factthat solar energy needs to be absorbed, and converted to a differentenergy form for utilization, the absorbing function and the convertingfunction being best conducted at locations remote from one another formost efficient energy conversion. The solar energy absorption processshould make most efficient use of the limited periods of maximumincidence of solar energy, i.e. exposure to direct sunlight. Theconversion process can equally well be conducted continuously,independently of the presence or absence of direct incident sunlight, sothat best overall efficiencies are accomplished by separately locatingthe absorbing and converting function. In this way, one function doesnot hinder or interfere with the other.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel solar energyutilization process.

It is a further object to provide a photochemical process for producinguseful chemical products which is economically attractive.

In its broad aspect, the present invention provides a means forutilizing radiation of wavelength from about 100 to about 750 nanometers(nm), e.g. natural radiation to effect photochemical reaction of achemical reactant to produce a chemical product therefrom, whilstsupported on a particulate carrier and dispersed over a wide area as amonolayer. The carrier material is in the form of discrete, small sizedlumps or modules, e.g. beads, or buoyant foam pieces which distributethemselves fully and evenly as a monolayer e.g. over the surface of abody of water, or in a dry shallow pan accompanied by shaking thereof,or as a fluidized bed, or under gravity-flow, cascade arrangements. Thereactant materials are carried and supported by the carrier materials insuch a manner that they are not chemically affected by the carrier butare exposed to solar radiation while supported thereby, and the productsformed by the photochemical reactions thereof are readily recoverablefrom the carrier material. While the carrier material, e.g. the floatingbeads, is inert to the reactants and products, the supporting body ofliquid may or may not involve in the photochemical reaction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a preferred embodiment of the invention, the particulate carriermaterial is supported as a mono-layer by floatation, on a liquid medium.The supporting liquid medium is preferably water, and the radiation issolar radiation. In one embodiment, the body of water is a moving bodyof water such as a natural or artificial lake, river, stream, reservoiretc. The carrier supporting the reactant is then conveyed, by thenatural or induced water flow in the body of water, to a downstreamproduct recovery location from a reactant receiving location, with thesolar energy absorption and photochemical conversion processes takingplace during conveyance of the carrier therebetween. The chemicalproduct so formed can be removed from the carrier following passage tothe product recovery location, and then if desired the carrier can berecycled from the reactant receiving location.

Most suitably, the carrier material is a mass of buoyant beads or discseach comprising a substantially water-insoluble, UV-stable polymer. Thusthe carrier may comprise hollow glass spheres coated with a suitablepolymer, optionally covered with a protective film of low oxygenpermeable polymer, or foam-cored plastic spheres provided with asuitable polymer coating. The water-insoluble, UV-stable polymer istreated, e.g. impregnated, with the reactant material so that it isswollen thereby but does not chemically react with the reactantmaterial. In similar manner the product formed by photochemical reactionof the reactant while impregnated in the polymer, is similarlychemically inert to the chosen polymer and extractable therefrom, butnevertheless remains supported e.g. impregnated in the polymer untilpositive steps are taken to extract the product from the carrier. Thetype of polymer is thus chosen in conjunction with the reactants to beused and the products to be formed, with a view to arranging suitableinertness, support and product extractability.

In the alternative, the carrier can comprise a buoyant plastic or otherfoam material, capable of releasably holding and supporting thereactants and products and exposing them to solar radiation whilefloating on water.

In another preferred embodiment of the invention, the floating carriermaterial on the body of liquid is covered by a solar radiation permeablebut substantially gas impermeable film or membrane. Then a selectedgaseous atmosphere can be provided, beneath the film in contact with thereactant material either to supply a reactant thereto or to protect thereactant or products from atmospheric effects e.g. oxygen.

The present invention can be put into practice in several ways. Forexample, it can be used for the production of useful organic chemicalcompounds by photochemical conversion of other organic compoundreactants. It can also be used for the collection and storage of solarenergy, by causing a reactant to convert photochemically to anenergy-enriched product from which energy can be obtained in one form oranother e.g. by reversing the chemical reaction in the absence of thesolar radiation, or by some other energy-releasing utilization of theproduct (fuel, hydrogen-source etc.)

BRIEF REFERENCE TO THE DRAWINGS

FIG. 1 is a cross-sectional view of a first embodiment ofpolymer-bearing bead useful in the invention.

FIG. 2 is a cross-sectional view of an alternative form ofpolymer-bearing bead useful in the invention;

FIG. 3 is a cross-sectional view of a further form of polymer-bearingbead useful in the invention;

FIG. 4 is a top plan view of another form of polymer-bearing bead usefulin the invention;

FIG. 5 is a cross-sectional view of the bead of FIG. 4;

FIG. 6 is a perspective view of a different polymer-bearing bead usefulin the invention.

FIG. 7 is a diagrammatic illustration of an embodiment of the process ofthe present invention.

FIG. 8 is a chromatogram of the products from Example 7 below;

FIG. 9 is a chromatogram of the products from Example 8 below.

SPECIFIC DESCRIPTION OF BEST MODES

FIG. 1 shows a cross-sectional view of one embodiment of the invention.The bead comprises a glass sphere 22 with a hollow interior 24. Thesphere 22 is surrounded by a layer of cross-linked, swellable polymer20, namely cross-linked polymethylacrylate.

The hollow sphere 22 acts as a buoyant particle surrounded by theswellable polymer layer 20 in which the photo chemically reactivereagents are retained and photochemically react on exposure to solarU.V. radiation.

FIG. 2 illustrates a form of bead suitable for use where thephotochemical reactions are inhibited by oxygen. It depicts a basicallysimilar bead as shown in FIG. 1 with glass sphere 22 and hollow interior24 surrounded by swollen polymer layer 20 in which the photochemicallyreactive reagent is contained, but also includes an outer thin film 26.Thin film 26 consists of a low oxygen permeability elastomer film thatallows reactions to occur in the swollen polymer in the absence ofoxygen, while permitting sufficient solar radiation to pass therethroughto reach polymer layer 20.

FIG. 3 shows another form of bead for use in the invention whichconsists of a spherically shaped bead with inner cross-linked expandedfoam core 32 surrounded by a cross-linked polymer layer 30. The foamcore 32 which contains air pockets and acts as a buoyant particle,similar to the hollow sphere in FIG. 1 described above, may be made ofany polymer stable to solar U.V. radiation for example, polystyrene,polyacrylonitrile or polymethacrylonitrile and is most easily preparedby irradiation of prefoamed polymer beads. Cross-linking of the foam,which is cause by irradiation, must be enough to prevent destruction ofthe foam when exposed to swelling solvents.

A further useful form of bead, depicted in FIG. 4 and in FIG. 5, is ofdifferent shape but is similar in construction to that of FIG. 3. It hasa flattened, disk-like shape, i.e. constituting a platelet. FIG. 5 showsthe cross-linked foam core 32 which is surrounded by a thin layer 30 ofcross-linked polymer. Both the core 32 and polymer layer 30 may be madeof the same materials as those described in FIG. 3. The shape of thisbead allows for a large area of exposure to solar radiation and thusefficient conversion of the reagents therein.

FIG. 6 depicts another form of bead for use in the invention. Theembodiment is a rod shaped bead with an inner core 42 surrounded by athin polymer layer 40. The core may be made of any foamed or unfoamedlow density polymer, for example polyethylene, and the polymer layer 40may be made of any of a variety of polymers as described herein. Solid,buoyant polymer rods are also useful.

The dimensions of the beads as shown above, will depend on the thicknessof the polymer layer which, in turn, depends on the extinctioncoefficient of reactive materials and their concentration in the polymerlayer. Preferred layer thicknesses are in the range of 0.1 mm to 2.0mm., though greater layer thicknesses are also suitable.

The beads may be easily handled using any man-made or natural reservoirof water on which the beads will float, and fluidized bed techniques.They may be pumped readily as slurries in water or other solvents. Thesize of the beads is variable though preferably the beads should be ofsmall size, suitably in the range of 0.2 to 5 mm. diameter.

The process of the invention contemplates the use of buoyant polymerbeads, which float on the body of liquid, normally water. The density ofthe body of water can be increased, if desired, to promote the buoyancyof the beads, by dissolving salts in the water (sodium chloride, calciumchloride etc.). Such salted solar ponds are known. This provides a meansby which normally non-water-buoyant polymer beads can be used as thecarrier for photochemical reactions.

After the beads have been exposed to solar U.V. radiation for a suitablelength of time to convert the reagents contained thereinphotochemically, they are removed from the water, for example byfiltration. Depending on the nature of the energy enriched or energyreleasing product in the bead, the useful products are removed from thebead, for example by distillation or solvent extraction, and the beadsare then recharged with fresh reagents, ready for re-use.

The exposure of the beads, and, consequently, of the reagents therein,may be controlled by controlling the rate of flow of surface water inthe reservoir. Moreover, the beads will automatically spread themselvesin a monolayer on the surface of the water, and, with sufficient waveaction, uniform exposure of the beads occurs.

An embodiment of the process of the invention is illustratedschematically in FIG. 7. This shows a body of water 50 flowing in thedirection of arrow A. Polymer-bearing, buoyant beads 52 of one of thetypes previously described, are fed to an impregnating vessel 54disposed at an upstream location relative to the body of water forreceiving chemical reactant. The reactant is fed to impregnating vessel54 via inlet 56 and impregnates the beads therein. The impregnated beadsare then poured onto the surface of the body of water 50, on which theyfloat and spread out as a monolayer, at the surface of the body of wateras illustrated, thereby exposing the reactant impregnated therein toincident solar radiation as indicated. The beads 52 are transported bythe moving body of water to a weir arrangement 58 over which the waterand beads fall into a screened receiving vessel 60 where the beads, nowimpregnated which chemical product are separated from the water byscreen 62 and fed to a product recovery vessel 64, where the chemicalproduct is separated from the beads, e.g. by solvent extraction, andrecovered via exit 66. The beads 52 are then recycled via line 68 forre-impregnation in vessel 54 with reactant and repeat of the cycle.

The polymer for use as the carrier for the reactants and products can bechosen from a wide variety of different polymers, having regard to thefunction which it is to perform. The polymer must be chosen with regardto its ability to retain the specific reactants and products in a stablebut readily recoverable manner, and without chemically reacting orinterfering with the reactants, products or course of reaction therein.Organic polymers and organic compounds generally show a reasonabledegree of compatibility with one another, with the compounds having asolubility in the polymers, to various extents. The polymer must bestable on exposure to UV and other solar radiations. It must besubstantially unaffected by water --where normally water solublepolymers are to be used, they are used in cross-linked form to importthe necessary water resistance. Preferred polymers are capable ofrepeated cycles of impregnation with reactant, floatation and productremoval, so that the beads used in the invention are re-usable manytimes over. Useful polymers can be chosen from among the following:

cross-linked polymethylacrylate;

cross-linked polyethylacrylate;

cross-linked ethylene-vinyl acetate copolymers;

cross-linked polyvinyl acetate;

cross-linked polyvinyl alcohol;

cross-linked polymers and copolymers of hydroxyethyl acrylate;

cross-linked polymers and copolymers of hydroxyethyl methacrylate;

cross-linked polymers and copolymers of hydroxyethyl ethacrylate;

cross-linked acrylamide polymers and copolymers;

cross-linked N-substituted acrylamide polymers and copolymers;

cross-linked polymers and copolymers of acrylonitrile;polymethacrylonitrile;

cross-linked ethylene-ethyl acrylate copolymers;

cross-linked ethylene-acrylic acid copolymers;

cross-linked ethylene-methacrylic acid copolymers; polystyrene;

poly (alphamethylstyrene) semi-crystalline polyethylene (optionallycross-linked);

semi-crystalline polypropylene (optionally cross-linked);

ethylene-propylene copolymers and terpolymers;

cross-linked silicone polymers;

fluorocarbon polymers e.g. polyvinyl fluoride and polyvinylidenefluoride;

polyvinylchloride (suitably stabilized to impart the necessary degree ofUv resistance) polyamides;

polyesters;

poly (amide-imides);

polyaminoacids, semicrystalline or cross-linked proteins;

cellulose and its derivatives;

polyurethanes;

polyepoxides;

cross-linked polyethylene oxide;

cross-linked polypropylene oxide;

polyisobutylene;

polyisoprene;

polybutadiene;

SBR copolymers;

chlorosulfonated rubbers;

rubber hydrochloride;

hydrogenated rubber;

cross-linked hydrogels.

Cross-linked polymers have the additional advantage that they swell to ahigh degree to provide for ready impregnation with reagents and removalof products.

Preferred polymers for use in the invention have a glass transitiontemperature below that at which the impregnation and extraction takesplace. If the polymer is in its glassy state, i.e. below its glasstransition temperature, the diffusion of the chemical into the polymeris hindered, so that impregnation is slowed. Above this temperature, themobility of the chemical reactants and products is enhanced, leading toshorter impregnation, recovery and reaction times, especially where abimolecular reaction is to be accomplished.

Specific preferred polymers are cross-linked ethylene-vinyl acetatecopolymers.

In one of its aspects, the present invention can be utilized as a meansof photosynthesis of organic chemicals. There are a number of usefulorganic chemical compounds whose only or whose most efficient synthesisinvolves a photochemically induced reaction. The present inventionprovides a simple and efficient means by which such reactions can beconducted using natural solar radiation and hence avoiding theconventional artificial lamp uses and exposures. In providingpharmaceutical products for example, especially those requiring achemical ring-forming or ring opening reaction, photochemical synthesisis often the preferred method.

A specific example of organic chemical synthesis which can be conductedby the process of the present invention is formaldehyde synthesis fromcarbon monoxide in the presence of water and metal complexes: ##STR1##To conduct this reaction according to the invention, polymer beads areimpregnated with carbon monoxide and an appropriate organic solublemetal complex, e.g. ferric carbonyl. Then they are floated on a body ofwater in exposure to direct sunlight, and formaldehyde and the metalcomplex catalyst subsequently recovered from the bead. The waterreactant can thus derive from the body of water providing floatation.The formaldehyde so formed is useful in a variety of purposes, includingconversion to methanol for use as a fuel. This reaction to produceformaldehyde is similar to natural photosynthesis. The choice of polymerin the bead for this reaction is made on the basis of criteriapreviously discussed--inertness to water, reactants and products,ability to hold but also to release readily the reactants and productsand the catalyst or photosensitizer necessary for the reaction,radiation transparency or translucency etc.

An alternative manner in which the process of the invention may beconducted, in using a gaseous reagent such as carbon monoxide, or inadopting a chemical reaction or compound which is sensitive to oxygen,is to cover the floating beads on the water surface with a solarradiation permeable membrane, under which is provided an atomosphere ofreactant or inert gas. The membrane may be supported by the atmosphereof gas beneath it, to exclude oxygen from the vicinity of theimpregnated floating beads or provide for their contact with a reactantgas.

The following are additional examples of organic chemical conversionswhich can be effected using the process of the present invention. Manyof these can be used as energy storage and conversion means, as noted.

(a) Cis-trans Interconversion of Stilbene

At the appropriate wavelength of U.V. radiation the trans-isomer ofstilbene will absorb energy and convert completely to the less stablecis-isomer: ##STR2##

Reconversion of the cis-isomer back to the trans-isomer will releaseenergy, as heat, that may be harnessed and utilized.

(b) Reduction of Quinones

Quinones undergo reversible oxidation-reduction reactions on exposure tosolar radiation: ##STR3##

Reduction by solar U.V. radiation exposure, of anthraquinone in thepolymer layer during the process of this invention, to 9,10-dihydroxyanthracene, involves the absorption of a specific quantityof energy, known as the reduction potential. The 9,10-dihydroxyanthracene may then be removed from the polymer bead andsubsequent oxidation will yield anthraquinone and energy. The reagentR--OH is normally water, and thus may be supplied by the suspensionmedium. In the above reaction, the photochemical conversion preferablytakes place in the absence of oxygen, so that it is conducted under aninert atmosphere e.g. of nitrogen or CO₂ gas trapped by a solarradiation permeable, gas impermeable blanket. In a subsequent step, thealdehyde is extracted, and the dihydroxyanthracene is treated withoxygen, e.g. while still on the beads, packed into a column. In suchtreatment, the dihydroxyanthracene is oxidized back to anthraquinone,with generation of useful quantities of hydrogen peroxide. Such aprocess can advantageously be conducted adjacent to a hydrogen peroxideuser, e.g. a pulp and paper facility, since the storage and shipping ofhydrogen peroxide is hazardous.

(c) Oxidation for an internally-unsaturated olefin

For example, squalene can be photochemically oxidized, in the presenceof oxygen and sunlight, to form a hydroperoxide derivative thereof whichis useful in a number of chemical reactions.

(d) Photochemical disproportionation of ketones

For example, ketones of hydrocarbons in which the ketonic group islocated at a non-terminal carbon atom of the hydrocarbon chain willdisproportionate on exposure to sunlight, to form smaller ketones andhydrocarbons by chain scission (Norrish reactions).

(e) Addition of singlet oxygen to various compounds using boundsensitizers

An example of such a photochemical process is the production of thefragrance "Rose Oxide", by photooxygenation of citronellol with rosebengal as sensitizer. Isomeric hydroperoxides are produced, which can bereduced to alcohols, rearranged and cyclized to rose oxide.

(f) Photosynthesis of vitamin D

7-Dehydrocholesterol (obtainable by known processes from cholesterol, anatural product readily available from, e.g. cod liver oil) undergoes aphotochemical ring opening process on UV irradiation to give previtaminD3, which on warming readily gives the thermodynamically more stablevitamin D₃ ##STR4##

The only commercial method of synthesis of vitamin D is photochemical,the current energy costs for which are substantial. Such a photochemicalprocess is advantageously conducted according to the present invention,since the steroid reactants and products are relatively high molecularweight and hence non-volatile on exposure to sunlight. They are suitablyimpregnated into and removed from an ethylene-vinyl acetate copolymer ascarrier.

Other photochemical synthesis of pharmaceutically useful steroids suchas the production of hydroxy derivatives of vitamin D₃ and theproduction of dydrogesterone (a sex hormone) form a pregnadienederivative, are also advantageously used in the present invention.

(g) Photoisomerization of vitamin A acetate

The industrial process for producing vitamin A acetate (Wittigsynthesis) produces a mixture of stereo-isomers, only one of which, theall-trans isomer is useful. The 11-cis form in the mixture can bephotochemically converted to the all-trans form by the process of thepresent invention.

Sensitizers used to promote photochemical reaction in the process of thepresent invention are compounds capable of absorbing solar radiation andtransferring it to the reactants, either radiatively or non-radiatively.The appropriate sensitizers may be chemically bound to the polymer layeror to the reactant, but removable from the product after the reaction iscomplete. They can if desired be left bonded to the polymer beads, ifthe beads are to be re-used in the same or similar reactions. They canbe bound to the polymer in a similar way to that of UV stabilizerscommonly used with polymers, or used in other ways analogously to knownpolymer stabilizer uses.

The types of products which can be synthesized according to theinvention, and the reactants which can be used, should have a relativelylow vapour pressure in order to be retained in the polymer films for therequired exposure times (anywhere from a few hours to, say, one month,depending upon the thickness of the layer and other factors). Where thereactants and/or products are normally unacceptably volatile, they canbe introduced into the polymer bead as a complex, which can be made togive up the product/reagent on demand, chemically or thermally. Theproducts and reactants should also be relatively stable to oxygen ifthey are to be exposed on open bodies of water. Use of beads of the typeshown in FIG. 2 can be used in instances of high oxygen sensitivity.

In another of its apsects, the present invention can be utilized as asolar energy collection and conversion means. As noted above, it can beused to conduct reversible chemical reactions which when reversed, yielduseful energy. In addition, however, the present invention can be usedto provide fuels for fuel cell utilization, and to generate and storehydrogen fuel.

As an example of such an aspect of the invention, thequinone-hydroquinone redox reaction may be considered. Under solarradiation and in the presence of water, benzoquinone is reduced tohydroquinone: ##STR5##

Hydrogen can be obtained by subjecting an aqueous solution of thereduced, hydroquinone compound to electric current, whereupon hydrogenis generated and the oxidised form benzoquinone is re-formed. Theelectrical power required to produce a standard amound of hydrogen fromsuch a hydroquinone solution is approximately half that required toproduce the standard amount of hydrogen by the normal process,electrolysis of water. Accordingly, the process of the present inventionprovides a means for obtaining hydrogen fuel using solar energy. Thereduced product can either be fed to a fuel cell and oxidized therein toobtain electrical energy, or treated to release hydrogen, in aneconomically efficient manner.

This process can also be viewed as a process for storing hydrogen, in achemically combined form. The generation of hydrogen gas in largequantities, ready for use as a fuel, poses serious storage problems,necessitating the use of pressurized, heavy storage tanks and cylinders.The storage of the hydrogen in chemically combined but readily availableform, e.g. as a hydroquinone, reduces such problems.

It will be understood that the quinone-hydroquinone reversible redoxreaction discussed above is merely a representative example of a redoxreaction which can be used for this purpose in the process of thepresent invention. The system can be generalized, as follows: ##STR6##Reaction (1) takes place in the floating polymer beads, according to theinvention, as previously described. A represents any organic compoundcapable of being photo-reduced in water. It is effectively acting as achemical "carrier" of hydrogen, for generation and utilization ofhydrogen. There are now two alternative reverse reactions to choose:##STR7## Reaction (2) produces hydrogen fuel which is subsequently usedin energy production. Reaction (3) produces electrical energy directlythrough fuel cell utilization. In either case compound A is regenerated,ready for recycling.

Additional examples of reversible redox couples which can bephotochemically reduced in the presence of water, and can hence be usedin the process of the present invention, are adenosinetriphosphate⃡adenosine diphosphate, and the aforementionedanthraquinone⃡9,10-dihydroxyanthracene.

A still further aspect of the present invention concerns nitrogenfixation. The plastic bead or foam system used in the present inventioncan be used to retain photocatalysts suitable for the fixation ofnitrogen from the atmosphere using natural sunlight as the source ofenergy, to form nitrogenous compounds useful as fertilizers. Suchcatalysts are normally transition metal catalysts. The nitrogenouscompounds are formed in the polymer of the bead itself, and can berecovered therefrom. Alternatively, the beads may be made of abiodegradable polymer, so that the combined beads and nitrogenousproduct can be utilized as fertilizer.

The economic features of the process of the present invention are highlyattractive, in comparison with the capital and energy costs ofconventional, silicon-based solar energy collectors and associatedconvertors. At the current state of the art, silicon solar cells costabout $100 per square meter of radiation-incident surface, not countinginstallation, transformer and transmission costs. A one-hectareinstallation thus costs $1,000,000. The actual costs of electricityproduced from such devices are estimated to exceed 20-50c perkilowatt-hour. In the present invention, 1 kg of polymer will cover 1square meter of pond surface to a thickness of 1 mm, which at 50c perpound of polymer calculates to a capital cost of about $10,000 to coverone hectare of water surface. Even at low energy conversionefficiencies, potential economic advantages of the present invention aresignificant.

The following specific examples illustrate the process of the invention.

EXAMPLE 1

Crosslinked ethylene-vinylacetate copolymer beads were prepared by thefollowing procedure. Ethylene-vinylacetate beads (500 g, ELVAX 150)containing approximately 33% vinylacetate were placed in a sealedvessel, evacuated and flushed with nitrogen. They were irradiated forthree weeks with γ-rays from a cobalt-60 source. The total dose requiredfor crosslinking was about 15 megarad. After γ-irradiation the beadswere placed in a Soxhlet extractor and extracted with toluene until nofurther soluble materials could be recovered. The beads were then driedunder vacuum at 40° C. and stored for future use.

EXAMPLE 2

Crosslinked ethylene-vinylacetate beads (10 g) were placed in a testtube along with 5 cc of a 2% solution of 2-undecanone in pentane. Thetest tube was stoppered and placed in a water bath at 35° C. After onehour all of the solvent had been absorbed by the beads. The beads werethen dried in air and exposed to outdoor sunlight by floating them on adeveloping tray containing water. After two days of exposure to outdoorsunlight, 15% of the 2-undecanone had been converted to octene.

EXAMPLE 3

Crosslinked ethylenej-vinylacetate beads (20 g) were placed in a flaskand gently agitated while 5 cc of a 2% solution of decanophenone wasadded. After agitating at room temperature for 30 min. all of thesolution was absorbed by the beads. The beads were removed, dried andexposed for three days floating on the surface of water in a flat dish.After exposure, the beads were placed in a container with 20 cc oftoluene. After standing for three hours, the excesss toluene wasdecanted and additional 20 cc was added. This procedure was repeateduntil no further product could be removed from the beads. The tolueneextracts were then analyzed by gas chromatography. The results indicatedthat substantially all of the starting material had been converted tophotoproducts of which the major product was acetophenone.

EXAMPLE 4

Crosslinked ethylene-vinylacetate beads (38g) were immersed in 100 ml ofsqualene sensitized with 5 mg of rose bengal dye. After 48 hr the beadswere removed and dried. Approximately 3.5 g of squalene had been takenup by the beads. The beads were floated over distilled water in a traycovered with a thin polyethylene film and were exposed to radiation froma sunlamp for six hours, after which they were removed from the surfaceof the water and extracted eight times with absolute methanol. Theamount of hydroperoxide was determined by the change in absorbance at260 nm when treated with triphenylphosphene. Based on the peroxideanalysis, 6.4% of the double bonds of the squalene had been converted tothe corresponding hydroperoxide. This procedure was repeated, exceptthat the samples were exposed to ultraviolet light on the roof of abuilding for three days. Based on UV analysis the conversion tohydroperoxide was 3%.

EXAMPLE 5

7-Dehydrocholesterol (0.046 g) were dissolved in 4 ml of anhydrousether. Crosslinked ethylene-vinylacetate beads (1 g) were added to thesolution After one hour all of the solution was absorbed by the beads.The beads were air dried. The concentration of 7-dehydrocholesterolremaining in the beads was approximately 5 wt-%. The beads were thenfloated on water in a tray and irradiated for a total of 48 hours innatural sunlight. The weather was cloudy during this period and verylittle direct sunlight reached the beads. After exposure, the beads wereextracted with ether and analyzed by obtaining the UV spectra. Based onthe UV analysis, approximately 60% of the 7-dehydrocholesterol had beenconverted to the previtamin D. Heating the ether solution of theprevitamin at 60° C. for two hours converted the previtamin to vitaminD.

EXAMPLE 6

Low density polyethylene beads approximately 2 mm in diameter (Tenite800E) were extracted with 95% ethanol in a Sohxlet extractor and dried.This polymer is non-crosslinked, and has limited crystalline regions 50g of the beads were placed in a flask with 20 ml 2-undecanone and heatedto 60° C. overnight. The amount of 2-undecanone absorbed was determinedby extraction of a small sample (2 g) with ethanol followed by G.C.analysis. Samples of the beads were floated on water in a photographictray and exposed for (1) 28 hrs, and (2) 60 hrs to natural sunlight. Afurther sample (sample 3) was exposed to a sunlamp for 16 hrs.

The exposed beads were collected, rinsed with water to remove surfacedust and dirt, then extracted 6-8 hrs with ethanol. The extracts wereanalysed by G.C. The conversion to octene and acetone was 18% for sample1, 40% for sample 2 and 35% for sample 3. The yield of acetone was lowerthan expected because of the loss of this volatile compound from thebeads.

EXAMPLE 7

7-Dehydrocholesterol (20.4 mg) was dissolved in ether (10 ml) and theresultant solution added to crosslinked ethylene-vinyl acetate beads (10g; approximate bead diameter 3 mm). The entire solution was absorbed bythe beads within 1/2 hour. Ether was removed from the beads by purgingwith N₂ for 1 hour.

A monolayer of the beads was placed in an evaporating dish andirradiated by an Optical Associates Inc. 500W xenon-mercury lamp(approximately wavelength emission range 250 nm to visible) for 15minutes. Nitrogen was flushed over the beads throughout the exposure. A0.45 g sample of the beads was extracted overnight with a 5 ml volume ofchloroform:hexane:tetrahydrofuran 70:30:1. The resultant solution wasanalyzed on a Waters model 6000A high performance liquid chromatographusing a chloroform:hexane:tetrahydrofuran 70:30:1 mixture as carriersolvent and a γ-porasil column. Detection was by a Waters Lambda-Maxmodel 481 Ultra Violet absorbance detector set at 254 nm. Earlierworkers, Tartivita, K.A., Sciarello, J.P. and Rudy, B.C., J. Pharm.Science, 65:1024 (1976) have used a similar analytical technique andhave identified the order in which the various photoproducts are eluted.The chromatogram shown in FIG. 8 shows the production of previtamin D₃,vitamin D₃ as well as tachysterol and lumisterol from this irradiation.On FIG. 8 intensity is plotted as ordinate against time as abscissa.Peak 68 represents previtamin D₃, shoulder 70 represents lumisterol,peak 72 represents tachysterol, peak 74 represents vitamin D₃ and peak76 unchanged 7-dehydrocholesterol.

EXAMPLE 8

A monolayer of beads loaded with 7-dehydrocholesterol as in thepreceding example, was placed in an evaporating dish, flushed with N₂and covered with a polyvinylidene chloride film (Saran Wrap). The beadswere exposed for 30 minutes to light from the OAI xenon-mercury lampused in Example 7. Extraction and analysis as in Example 7 produced thechromatogram of FIG. 9, similar to FIG. 8. Peak 78 represents previtaminD₃, shoulder 80 represents lumisterol, peak 82 represents tachysterol,peak 84 represents vitamin D₃ and peak 76 is unchanged7-dehydrocholesterol.

EXAMPLE 9

Crosslinked ethylene-vinyl acetate beads loaded with7-dehydrocholesterol as in Examples 7 and 8 were placed in anevaporating dish as a monolayer and covered with two layers ofpolyvinylidene chloride film. They were then exposed to solar radiationfor 5 hours and subsequently extracted and analysed as in Examples 7 and8. Product analysis showed a 38% conversion of starting material, 0.85%production of previtamin D₃. The remaining previtamin was converted toother products via oxidative side reactions.

EXAMPLE 10

Foamed silicone beads containing rose bengal were prepared as follows. Amixture of 10 parts silicone prepolymer (General Electric RTV 615A), 1part catalyst (General Electric RTV 615B) and 0.15 parts rose bengal(British Drug Houses Ltd.) was allowed to fall dropwise onto a heatedteflon coated metal surface. The droplets polymerized upon contact.

A solution of citronellol in methylene chloride was poured over thebeads, with the beads readily absorbing all the solution. Removal of themethylene chloride by evaporation left beads loaded with 33.3 mgcitronellol/gram beads. These beads were arranged as a monolayer on anevaporating dish, placed on ice 71/2" from a 200 watt incandescent bulbemitting visible light and irradiated for varying periods of time.Analysis for hydroperoxide product using standard techniques (Stein,R.A. and Slawson, V., Analytical Chemistry, 35: 1008 (1963)) gave theresults in Table 1.

                  TABLE 1                                                         ______________________________________                                                    hydroperoxide detected                                            Irradiation time                                                                          (as % of maximum theoretical yield)                               ______________________________________                                        1 hour      64.5                                                              3 hour      81.1                                                              11 hour     100.0                                                             ______________________________________                                    

EXAMPLE 11

Silicone beads prepared and loaded with citronellol as in Example 10were floated on water and exposed to solar radiation for 1 hour.Analysis for hydroperoxide showed a degree of conversion of 29.2% (as apercentage of the maximum theoretical yield).

EXAMPLE 12

Silicone beads prepared and loaded with citronellol as in Example 11were floated on a 20% calcium chloride aqueous solution and exposed tosolar radiation for 1 hour. Analysis for hydroperoxide showed a degreeof conversion of 14.6% (as a percentage of maximum theoretical yield).

I claim:
 1. A process for converting at least one photochemicallyreactive chemical reactant to photochemical reaction products utilizingradiation of wavelength from about 100 to about 750 nm, whichcomprises:providing a carrier which is substantially inert to thechemical reactant and the photochemical reaction products; applying saidat least one reactant to the carrier and supporting it thereon ortherein; floating said carrier supporting said at least one reactant ona liquid medium in which the carrier is substantially insoluble andinert; covering the carrier while floating on the medium with a film ofsubstantially gas impermeable, solar radiation permeable material and byexposing the covered carrier-supported reactant or reactants toradiation of wavelength from about 100 to about 750 nm while the carrierfloats on the liquid medium; and recovering from the inert carrierphotochemical reaction products obtained from said reactant orreactants.
 2. The process of claim 1 wherein the liquid medium is anaqueous medium.
 3. The process of claim 2 wherein the radiation is solarradiation.
 4. The process of claim 3 wherein said inert carrier is awater buoyant bead comprising a substantially water insoluble, UV-stablepolymer, said reactant being supported on the carrier by impregnatingthe polymer with the reactant.
 5. The process of claim 1 in whicngaseous reactant for photochemical reaction with said reactant appliedto the carrir is retained below said film.
 6. The process of claim 1 inwhich a gaseous blanket of inert gas or gases is retained below saidfilm.
 7. The process of claim 6 wherein the chemical reactant isanthraquinone.
 8. The process of claim 2 wherein the supporting aqueousmedium contributes a reactant to the photochemical reactions.
 9. Theprocess of claim 1 wherein the chemical reactant is aninternally-unsaturated olefin.
 10. The process of claim 9 wherein theolefin is squalene.
 11. A process for converting at least onephotochemically reactive chemical reactant to photochemical reactionproducts utilizing radiation of wavelength from about 100 to about 750nm which comprises:providing a particulate, discrete-moduled carrierwhich is substantially inert to the chemical reactant and thephotochemical reaction products; applying said at least one reactant tothe carrier and supporting it thereon or therein; distributing thecarrier supporting said at least one reactant as a monolayer of carriermodules; exposing the carrier-supported reactant, while the carrier isdistributed as a monolayer to direct radiation of said wavelength fromabout 100 to about 750 nm so as to cause photochemical reaction of saidreactant to form a product; and recovering the product so formed fromthe inert carrier modules.
 12. The process of claim 11 wherein thecarrier is distributed as a monolayer by floatation thereof on a body ofliquid to which the carrier is inert.
 13. The process of claim 12wherein the body of liquid is aqueous.
 14. The process of claim 13wherein the carrier modules float on top of the body of aqueous liquid.15. The process of claim 14 wherein the radiation is direct solarradiation.
 16. The process of claim 11 wherein the carrier isdistributed as a monolayer by spreading over a shallow pan surface.